(1) Field of the Invention.
The present invention relates to apparatus for joining thermoplastic frame elements. More particularly the present invention relates to welding machines for welding corners or joints of frames such as window and door frames.
(2) Brief Description of the Prior Art.
Prior to the use of plastics in the manufacture of window and door frames, both wood and metal were used for making such frames. The frame elements (i.e. stiles and rails), when made out of wood, were secured by either an adhesive, nails, screws or some other connector, or a combination of two or more of the holding or connector components. When metals were used for the frame elements, the pairs of frame elements were connected and held together by welding, screwing or crimping the corners together.
The welding of structural metal frames for support of equipment is well known. Elements of a frame are cut to size and contour, and positioned together to form a corner. An insert is usually welded to both elements to hold them in position, thus forming a corner. Some of the frame elements are very heavy and sometimes require the use of auxiliary tables on which to initially locate the ends of the frame elements or sections to be welded.
Later, elements of the frame are secured and supported on pivotable clamps which are adapted to lock into place and firmly hold the elements of the frame in proper relationship to each other in preparation for welding. Such a fixture is more completely described in U.S. Pat. No. 3,054,887 issued Sept. 18, 1962.
Metal has also been used in the manufacture of window frames, but the stiles and rails are of substantially lighter weight metal than that used in structural frames. However, since the frame elements have to be rigidly held in position for joining them to form the corners, essentially the same type of equipment used to form structural frames is used to form the much lighter window frames, except that the equipment itself is scaled down in size and capability.
With the development of stronger plastics, such as vinyl compounds, for example, window frames and door frames have been made from plastic elements. With the use of such lighter plastic elements, light weight simple jigs may be used to support and hold adjacent elements of the frames in position to be welded.
Commercial equipment is available which welds plastic elements of a window or door frame together to form one or more corners of the plastic frame. Single point and multi-point welding machines provide means for fusing the ends of the same plastic frame together to form one or two corners, respectively. However, where technology has advanced in the materials used, the handling of the elements forming the frames has not kept pace with the advancement in such materials. Conventional equipment does not permit the welding of more than one frame in a single operation.